The present invention relates in general to motor vehicle headlamp systems, and, more specifically, to method and apparatus for aiming headlamps.
Motor vehicles use headlamps to illuminate the road. One or two pairs of headlamps are typically mounted at the left and right front sides of the vehicle. For example, a pair of low-beam headlamps and a pair of high-beam headlamps are used on some vehicles. Other vehicles may employ a single pair of headlamps that are electrically controlled to provide either low-beam or high-beam illumination.
Various regulations specify the light patterns that are to be produced by the headlamps. In particular, a beam cutoff (i.e., an upper border between illumination falling above and below a particular intensity) must be located at a certain height above the ground at a specified distance in front of the vehicle. In order to ensure compliance with regulations, headlamp mountings are made adjustable in order to aim the light beams as required. In general, a vehicle under test is positioned in a certain position relative to a test surface or measuring device, the headlamps are illuminated, and the resulting light pattern is analyzed. Based on the analysis, the headlamp mounting is adjusted either manually or automatically to obtain the desired position of the light beam. Headlamp aiming equipment (i.e., aimers) are available which employ either projection analysis or direct measurement of the beam cutoff. Robotic mechanisms may be used for performing automatic adjustments.
Headlamps must be properly aimed at the manufacturing plant during assembly of the vehicle. Vehicle manufacturers have found that improper aiming of headlamps may be observable to car buyers even when the aiming of the beams meets regulatory requirements. Regulations typically allow beam cutoffs to fall within a specified range of heights. Differences in aiming between a right-side headlamp and a left-side headlamp within the allowed range may be a source of dissatisfaction to the vehicle customer.
The criteria used in the aiming process includes a “buy-off window” for defining the acceptable values for a cutoff height. An aimer measures the current cutoff height of a headlamp and compares it to the buy-off window. If outside the window, an adjustment is made (either manually or automatically) and the height is re-measured. Once the measured cutoff falls within the buy-off window, the headlamp is disconnected from the aimer and the other headlamp of the pair can be checked. The term “aimer” typically refers to a device that measures a cutoff height. The aimer or a separate peripheral computing device determines any difference between the measured height and a pre-programmed desired height. For manual adjustment, the aimer may visually display the height discrepancy or the correction to be made. For automatic adjustment, an electronic message containing the correction is sent by the aimer or computing device to a robotic adjuster.
The vertical size for the cutoff window is selected to ensure that the cutoff is within regulations. Conventionally, the buy-off window is of a fixed size and a fixed distance from the ground. A window size small enough to ensure regulatory compliance may be large enough to allow a noticeable difference between cutoffs to remain present. Reducing the window size can lower any remaining differences between the sides. However, a smaller window size requires more expensive equipment both for measuring the height (e.g., the aimer) and for adjusting the headlamp mount (e.g., robotics) because of the more precise tolerances required. For example, more precise optics must be used and a smaller adjustment increment must be supported by the adjuster. In addition, aiming would take longer to complete which is particularly undesirable in a vehicle assembly line process.